The present invention relates generally to optical filters and more particularly to a method for making interference filters.
A traditional interference filter is produced by stacking, typically by depositing, many layers of dielectric thin film materials horizontally on a glass substrate. The thickness and the types of materials of these thin films may vary depending on the application. In general, the films are alternating and equal to m*xcex/4 in thickness, where m is an odd integer number. For a narrowband filter, the number of layers can be as high as 100.
FIG. 1 (background art) is a cross section side view of a traditional interference filter 1, made according to conventional manufacturing processes. The interference filter 1 has a plurality of dielectric material layers 2 deposited on a glass substrate 3. The number of the material layers 2, and the materials used in them, may vary from one application to another. In FIG. 1 the material layers 2 are depicted as being of four different materials 2a-d. To represent the operational characteristics of the interference filter 1, as a laser beam 4 is shown with its angle of incidence purposely skewed to show how reflected beams 5 are produced at each interface of the material layers 2.
Many factors affect the result of the thin film deposition processes currently used in manufacturing interference filters. These include: absolute thickness, evaporation rate, background gas pressure, tooling factor, coating material structure, temperature, etc. During the thin film deposition process, the substrates cannot be removed from the coating chamber for inspection and information on the source of error cannot be traced if the final result deviates from expectations.
Unfortunately, in conventional interference filter manufacturing the final results often deviate far from reasonable manufacturing expectations. From the information which the inventors are aware of, and this is admittedly somewhat limited because many manufacturers keep such information proprietary, the overall current average yield in narrowband filter manufacturing today is less than 30%.
Such a yield contrasts markedly with that in some other industries. For example, semiconductor microfabrication, where an average yield of 80% is normal. In general, semiconductor microfabrication processes have reached a mature stage and manufacturing yields are thus quite satisfactory. Dimensional control is very good, and can reach 0.25 microns or even smaller. There have also been thorough studies of photolithography, material deposition, etching processing, etc., as are widely used in semiconductor microfabrication.
It therefore has been the inventors"" observation that improved interference filter manufacturing processes are desirable. Preferably, such improved processes should produce interference filter manufacturing yields closer to those common for matured technologies, such as semiconductor microfabrication.
Accordingly, it is an object of the present invention to provide improved processes to fabricate interference filters.
And another object of the invention is to provide such processes which particularly provide a high yield of interference filters.
Briefly, one preferred embodiment of the present invention is a method for fabricating an interference filter. A substrate is provided. A working region is then defined with respect to the substrate. Finally, a plurality of layers of coating materials are constructed vertically in the working region, relative to the horizontal substrate.
Briefly, another preferred embodiment of the invention is an interference filter made by the method for fabricated, described above.
An advantage of the present invention is that it provides multiple, flexible, and combinable approaches to fabricating interference filters.
Another advantage of the invention is that it may facilitate quality review throughout fabrication, and thus problem identification and correction, and improved yield and end product quality.
Another advantage of the invention is that it may employ already well known and widely used manufacturing processes and materials, adopted from conventional electronic semiconductor integrated circuit (IC) and micro electromechanical system (MEMS) manufacturing. Highly desirable attributes of such processes may thus be imparted to the inventive processes and the products produced there with, including mass automated manufacturing, rigorous quality control, high yields, and low cost.
And another advantage of the invention is that it permits easy, very high integration with other products of conventional micro manufacturing processes.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the several figures of the drawings.